This invention relates to a wear-resistant sintered ferrous alloy for parts subjected to rubbing friction and a method of producing the same.
A typical example of metal parts that are forced to make continuous rubbing contact with another metal part is the rocker arm of an internal combustion engine. The body of the rocker arm is formed by casting or by forging, but the tip part where the rocker arm makes rubbing contact with a cam must be afforded with high wear resistance. Therefore, it is usual to harden the tip portion of the rocker arm by a surface treatment such as carbrizing, nitriding, chromium plating or plasma-spraying of a hard coating material, or alternatively to form the tip part separately from the main part of the rocker arm by chilled casting or by a powder metallurgy method and attach the tip part to the rocker arm body by soldering or by insert-casting.
As the performance requirements to the recent internal combustion engines for automotive uses have become more and more severe, there is the tendency to force the rocker arms to make rubbing contact with the cams under severer conditions. Then there arises a problem that the rocker arm tip parts produced by conventional materials and techniques and/or the cam surfaces undergo intolerably significant wear.